允许用户使用自定义的http.Client?

如下的代码中使用了硬编码的http.Client，能否使其允许调用方可以传递自定义的http.Client?
````
func (c JDCloudClient) doSend(method, url, data string, header map[string]string, timeout time.Duration, sign SignFunc) ([]byte, error) {
	client := &http.Client{Timeout: timeout}

	req, err := http.NewRequest(method, url, strings.NewReader(data))
	// ... 
}
````
